Thread: Tool Post Grinding

Hi Bob
Haven't used a tool post grinder but have used surface and cylindrical grinders.
Did you lock your gibs?
Did you make sure the wheel is tight?(Yes I know "they cant come undone", but they can, even on a Jones and Shipman)
After that I'm pretty much out of ideas sort of the bearings being shot.

Stuart

Ensure that everthing is tight and that the centre of the grinding wheel is no higher than the centre of the work-piece, best to be a little lower rather than higher.

Also how did you dress the wheel?

Thanks very much for the replies, Stuart and Metmachmad.

I had not tightened either the cross or compound slide so that's the first thing I will do tomorrow when I have another go.

The spindle bearings were trashed when I bought the grinder. I replaced them with Barden angular contact bearings which have a speed limit in oil of twice the grinder's maximum of 38,500 rpm. Setting the bearing preload was guess work, so if I have that wrong there could be another source of chatter.

I dressed the wheel with a diamond tool in a less than perfect Dumore holder.
I will redress to wheel tomorrow in a far more rigid tailstock mounted holder.

I had the grinder spindle set on the lathe centreline.

I will report the outcome of my attempt tomorrow.

Regards Bob.

How much did the bearings cost?
Did you feel the bearing after your test? If they arent warm you should be able to tighten them up. Bearing life goes down pretty fast as preload goes past a certain point, but the bearings will warn you by getting hot. Also if the bearings are cheap enough even with alot of preload they will likely last more hours than you'll put on them as a tool post grinder(unless of course you plan on using it alot).
Good luck tomorrow
Stuart

Two hundred bucks cash for the pair.

They don't get hot. The rear bearing gets warmer than the front bearing because of the belt tension. I replaced the oiling wicks and felts within the spindle housing when I replaced the bearings.

The preload was based on maintaining the position of preloading device as installed against the original New Departure bearing.

Regards
Bob.

Bob, where'd you get the Bardens? Abec 7 or 9?

Greg

Originally Posted by Anorak Bob

Two hundred bucks cash for the pair.

Ok so we go a little easy on the preload then


Stuart

Greg,

The bearings were ordered in for me by Statewide Bearings in Perth.
They are FAG / Barden Aerospace 200HC bearings.

In their catalogue, they state that they manufacture spindle and turbine bearings to class ABEC 9 and instrument bearings to class ABEC 7. The box the bearing came in is marked B7200C.T.P4S.UL. The P4S refers to tolerances as per DIN 628-6. I haven't bothered to go there.

Given the cost, you'd think they would do the job.

Bob.

Bob...I did some comparative research awhile ago but it looks like I'll need to review.

A friend in the industry told me that they suspect that any bearings are only of stated quality in the factory until they go to shipping, then every step removes some of the fanciness from them. Barden is the only manufacturer that I saw listing the elusive Abec 9 bearings, (ultra precision in the 60's lexicon).

I need to get a pair of AC bearings for my lathe soon, hence the question.

I have the New Departure bearing handbook (50's?) that shows the relationship between life, accuracy and preload. The famous Moore Jig Bore machines of the day used ABEC 9 spindle bearings cranked down so tight they were in the annual replacement range.

Greg

Barden supplies what is supposed to be a pretty good spindle rebuilding video but I've had no luck getting a copy here.

Maybe I have a problem with the preloading.

I placed a tenth indicator on the spindle with the magnetic base affixed to the spindle housing. There is about .0001" TIR runout which could simply be wear on the shaft BUT with pressure exerted with thumb and forefinger, I can move the spindle radially, about .001". This is with the spindle cold.

Do I crank up the preload adjuster?

Bob.

I would tighten it a little and then run it keeping an eye on the bearing temperatures. I had to do this with my mill recently and it's the only way to do it.
It should be warm to touch after around half hour, but not that hot you cant hold your hand on it.

Dave

Not that I disagree with Dave, but I came across this on the SKF site when looking for some info on preload "SKF angular contact ball bearings undergo a special heat treatment. When fitted with a steel, brass or PEEK cage, they can operate at temperatures of up to +150 °C. ".

Didnt come up with much about preload though some unlabeled graph I dont understand.

Mine are different being taper bearings, but only getting them hot enough to touch by hand will be insurance that you don't cook them or do any damage as they are expensive.
I know the SKF site say so, but I personally I wouldn't run them up around 150 °C.

Dave

The topic of preload and how to measure it occupied me for quite some time a coupe of years back, and my figurative ears would perk up whenever the topic was mentioned. Absent any kind of torque setting (or a torque wrench adapter for that matter) I guess for us it boils down to temperature rise.

I thought had read about 65º for a target somewhere, but from what Dave posted I guess the temp maybe is limited more by the spindle application* than bearing life. (and lube too...mine are greased with Kluber Isoflex 15 which has a 130º max temp.)

* I wouldn't want my lathe spindle to grow that much in a facing operation for example. 150º means a lot of movement.

Greg